Instant start electronic ballast with universal AC input voltage

ABSTRACT

The present invention relates to an electronic ballast that energizes fluorescent lamps connected in a parallel configuration. The ballast employs a power factor correcting boost converter that can be used over a wide range of AC line voltages to provide regulated power to a self-oscillating sine wave inverter that drives the fluorescent lighting load at high frequencies. The inverter employs special networks that limit a certain type of shoot-through current, and thus improve the efficiency of the unit. Also included is a restart circuit that limits power losses during the zero lamp condition, by periodically interrupting the inverter operation when the zero lamp state is detected. To improve operation of the power factor correcting circuitry over the wide range of AC line voltages, a DC offset is added to the sampled AC voltage at the higher AC line voltages by Zener diode based coupling circuit.

REFERENCE TO PREVIOUSLY FILED APPLICATIONS

This patent application is a continuation of and claims priority fromU.S. Provisional Patent Application No. 60/368,857 filed on Mar. 29,2002.

FIELD OF THE INVENTION

The present invention relates primarily to electronic ballasts, and moreparticularly to energy efficient instant start electronic ballasts thatoperate over a wide range of AC input voltages.

BACKGROUND OF THE INVENTION

With the increased interest in energy conservation, lighting systemsthat use less energy and are easy and cost-effective to install arebecoming more important. This conclusion is apparent when one considersthat lighting uses about 30% of the energy consumed in the UnitedStates. An effective method of reducing energy consumption that has beenfound by the lighting industry is to employ electronic ballasts thatenergize the lamps with high frequency alternating currents, operatingat frequencies in the 20 kHz to 100 kHz range. Electrical energy in thisfrequency range is efficiently generated by use of sine wave invertercircuitry that converts a DC voltage into the high frequency sine wavepower that is coupled to the lamps.

An instant start electronic ballast does not employ any filament preheatmechanism to assist in thermionic emission from the lamp electrodes, butrelies upon sudden application of a high voltage between the lampelectrodes to ignite the gas discharge within the lamp. Thus, in aninstant start ballast, the ballast circuit must provide a high voltageinto the open circuit load that the lamps present before they areignited. However, after ignition the lamp impedance changes to a lowvalue. This low value of impedance becomes even lower with increasinglamp current, a property of gas discharge electrical loads. Thislowering of the lamp impedance with current, known as negativeresistance, can cause circuit instability unless an impedance known asthe ballast impedance is placed in series with the lamp load. Thepresence of the ballast impedance helps maintain stable operation, andalso plays a role in determining the final lamp current.

For a ballast to operate over a wide range of line voltages, apre-converter stage may be employed that boosts the incoming voltage toa value higher than the peak value of the highest AC voltage that theunit will use. This pre-converter also known as a boost convertertypically uses an industry standard integrated circuit to perform thispower conversion in a way such that the AC load current follows theincoming AC line voltage. This methodology, known as Power FactorCorrection (PFC), greatly improves the electrical power factor of theincoming AC current. In a large lighting installation this is animportant feature as it reduces the amount of re-circulating reactivepower in the building wiring and the electrical utility transformers andfeeders allowing more useful power to be transmitted through theelectrical transmission of the utility company. Power factor correctioncircuits in prior art ballast circuits can have difficulty in properlyoperating over the wide or universal AC input voltage range. A circuitthat shifts a sampled voltage input in a power factor corrector chip toa more linear region of the chip characteristics would improve theoverall performance of the ballast.

The output of the PFC boost converter in an electronic ballast is a DCvoltage whose value exceeds the peak value of the highest AC voltagewithin the operating range of the ballast. An inverter stage is used toconvert this DC voltage into the high frequency sine wave voltagerequired to operate the lamps efficiently. An inverter that isfrequently used for instant start ballasts is a self-oscillating halfbridge circuit that is current fed through an isolation choke. A causeof heating of the transistor switches in this type of inverter is aparticular type of shoot-through current that occurs during the briefswitching interval when the transistors switch from one being on to theother being on. This heating becomes larger when reduced power is beingconverted, such as occurs with shorter lamps are used, or when thenumber of lamps is reduced. Circuitry that reduce the size of theshoot-through current, and reduces circuitry power losses in theinverter would improve the overall performance and the reliability ofthe ballast.

During conditions of operation when no lamps are connected to theballast circuit, overheating of the inverter components may occur. Toreduce the overheating in this condition and thus improve the overallperformance and the reliability of the ballast, power to the inverter iscyclically switched ON and OFF under control of a zero lamp sensecircuit. When a new lamp is installed, normal operation is resumedwithout disconnection and reconnection of the AC power source as isrequired by some designs. This provides for the ability of lamp changingwithin a facility without the need of turning lamps ON and OFF.

Examples of such prior art are shown in the examples that follow.

U.S. Pat. No. 5,177,408, granted Jan. 5, 1993, to A. Marques, disclosesa startup delay circuit for an electronic ballast for “instant start”type fluorescent lamps of the type having an electronic converterpowered by an active electronic preregulator. The converter is ainductive-capacitive parallel resonant, push-pull circuit or any othertype of current fed power resonant circuit. The preregulator may be of aboost type—the startup circuit may be either resistor and Zener diode,or resistor, capacitor and Diac network or programmable unijunctiontransistor circuit connected between the preregulator output and anoscillator enabling input of the converter.

U.S. Pat. No. 5,214,355, granted May 25, 1993, to O. K. Nilssen,discloses an instant start electronic ballast is comprised of a firstand second AC output voltage, where the second AC voltage is delayedroughly 90 degrees from the first AC voltage, which results in thevoltage across the tank inductor being approximately sinusoidal inshape. A first and a second fluorescent lamp are connected in serieswith the first and a second ballast capacitor, respectively and thetwo-lamp capacitor series combination are connected in parallel acrossthe inductor, thereby resulting in a sinusoidal current being providedto the lamps.

U.S. Pat. No. 5,559,405, granted Sep. 24, 1996, to Hubin [0081]otohamiprodjo, discloses a ballast for operating a gas discharge lamphaving a voltage boost, a half-wave bridge inverter and a parallelresonant circuit. An inverter control inhibits operation when the poweris initially applied to the ballast.

U.S. Pat. No. 5,834,906, granted Nov. 10, 1998, to J. Chou, et al.,discloses an electronic ballast for driving a fluorescent lamp whichincludes an EMI filter and power circuit, a preconditioner coupled tothe EMI filter and power circuit, and an inverter circuit coupled to thepreconditioner for energizing the fluorescent lamp. The preconditionerincludes an active power factor controller and a boost circuit that iscontrolled by the active power factor controller. The active powerfactor controller has a reference voltage input to which is applied areference voltage. At the startup, the inverter applies a time varyingsignal that is rectified. At least a portion of the rectified signal isfed back to the reference voltage input of the active power factorcontroller to boost the reference voltage to a level above normal sothat the active power factor controller will cause greater current toflow through the boost circuit, causing the boost circuit to generate aDC rail voltage more rapidly, which rail voltage is provided to theinverter circuit to ignite and operate the fluorescent lamp.

All of the above referenced prior art, disclose instant start electronicballast circuitry for use with fluorescent lamps. However, none of theprior art teach the use parallel connected lamps that operate over awide applied operating voltage range; lamps that can be disconnectedwhile the AC line voltage source is applied.

What is needed is an energy efficient instant start electronic ballastthat is capable of operating a plurality of parallel connected gasdischarge lamps that can be operated over a wide range of applied ACvoltages and having an automatic restart capability without interruptionof the power source. In this regard, the present invention fulfills thisneed.

It is therefore an object of the present invention to provide an instantstart electronic ballast for fluorescent lamps that can be used over awide or universal range of applied AC line voltages while maintainingadequate power factor correction over the entire range of operatingvoltages.

It is an additional object of the present invention to provide properoperation of an electronic ballast having a plurality of lamps connectedin parallel, so that light is still produced when at least one lamp isconnected to the ballast.

It is another object of the present invention to provide efficientoperation of an electronic ballast sine wave inverter circuit, even withsmaller lighting loads.

It is a still further object of the present invention to provide forreduced power consumption of an electronic ballast when no lamps areconnected to the ballast.

It is a final object of the present invention to ensure that theelectronic ballast provides for the automatic restart of operation whena lamp is installed, without disconnecting the applied AC power source.

SUMMARY OF THE INVENTION

The present invention describes an electronic ballast that energizesfluorescent lamps in a parallel configuration. The ballast employs apower factor correcting boost converter that can be used over a widerange of AC line voltages to provide regulated power to aself-oscillating sine wave inverter that drives the fluorescent lightingload at high frequencies. The inverter employs several novel specializednetworks that limit a certain type of shoot-through current, and thusimproves the efficiency of the unit.

Also included is a restart circuit that limits power losses during thezero lamp condition, by periodically interrupting the inverter operationwhen the zero lamp state is detected. To improve the operation of thepower factor correcting circuitry over the wide range of AC linevoltages, a DC offset is added to the sampled AC voltage at the higherAC line voltages by a Zener diode based coupling circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the invention may be obtained by referenceto the accompanying drawings when taken in conjunction with the detaileddescription thereof and in which:

FIG. 1 is a block diagram of a typical ballast circuit.

FIG. 2 is a partial schematic drawing that shows the rectifier and EMIfilter section of a typical ballast.

FIG. 3 is a partial schematic drawing illustrating the boostconverter/power factor correction circuit of the prior art.

FIG. 4 is a partial schematic diagram of the sine wave inverter sectionof a ballast of the prior art.

FIG. 5 is a schematic diagram detailing the boost converter/power factorcorrection circuit of the preferred embodiment.

FIG. 6 is a schematic diagram of the sine wave inverter section of aballast of the preferred embodiment.

FIG. 7 shows the sinusoidal waveform illustrating the performance of thecircuit that causes periodic cycling of the power to the sine waveinverter when a condition of zero lamps is sensed.

FIG. 8 is a schematic diagram that details a problem that sometimesoccurs in the prior art sine wave inverter of FIG. 4.

FIG. 9 details the use of resistor 82 and diode 81 of Outline 78 and theuse of resistor 84 and diode 83 of Outline 79 to minimize parasiticcurrents as used in the preferred embodiment.

FIG. 10, the preferred embodiment, is essentially the same as in theschematic shown in FIG. 8, except for the addition of Outline 78,comprising resistor 82 and diode 81, and Outline 79, comprising resistor84 and diode 83, to minimize parasitic currents.

FIG. 11 is a schematic diagram detailing the Power Factor Correctingcircuit being controlled during the zero lamp condition.

A better understanding and appreciation of these and other objects andadvantages of the present invention will be obtained upon reading thefollowing detailed description of the preferred embodiment when taken inconjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Generally speaking, the present invention is an electronic ballast thatenergizes lamps in a parallel configuration. The ballast employs a powerfactor correcting boost converter that can be used over a wide range ofAC line voltages to provide regulated power to a self-oscillating sinewave inverter that drives the fluorescent lighting load at highfrequencies. The inverter employs several novel specialized networksthat limit a certain type of shoot-through current, and thus improve theefficiency of the unit. Also included is a restart circuit that limitspower losses during the zero lamp condition, by periodicallyinterrupting the inverter operation when the zero lamp state isdetected. To improve the operation of the power factor correctingcircuitry over the wide range of AC line voltages, a DC offset is addedto the sampled AC voltage at the higher AC line voltages by a Zenerdiode based coupling circuit.

Referring first to FIG. 1, there is shown a block diagram that shows thepower flow of a typical ballast. AC power that is connected to terminals10 is converted to high frequency power and applied to a plurality offluorescent lamps connected in parallel, 14. Element 11 contains the acline filter to reduce EMI emission conducted onto the power line. Italso contains the AC rectifier that converts the AC sine envelope into apulsating DC waveform, 15. Element 12 is the boost power factorconverter stage (PFC). The PFC stage converts the pulsating DC waveformto a steady DC voltage, 16, while drawing a sine wave current from thepower line that matches the AC line voltage. Power factor correction isdesirable since lighting is often one of the largest electrical loads ofa large commercial building. Having the load current match the linevoltage maximizes the efficiency of the electrical utility'sdistribution system. The boosted DC voltage exceeds the maximum value ofthe pulsating DC waveform. The DC voltage is applied to the sine waveconverter 13 that change the DC voltage back into a sine wave voltage,but at a much higher frequency than the applied power AC voltage. Theinverter circuit applies the high frequency voltage to the lamps througha high impedance. A sufficiently high impedance is required to providestable operation of the fluorescent lamps, 14.

FIG. 2 shows a schematic diagram of the AC electromagnetic interference(EMI) filter and rectifier, 11. AC voltage applied on terminals 10passes through fuse 17 to the EMI filter which consists of capacitors 18and 20 and common mode choke 19. Varistor 21 suppresses any transientvoltage spike waveforms that may occur on the incoming AC voltage due tooperation of nearby electrical motors, or lighting strikes. The fullwave bridge rectifier 22 changes the AC voltage to a pulsating DCvoltage that is applied to node 15. Capacitor 23 serves as a highfrequency bypass capacitor for the high frequency switching currents bythe following PFC circuit.

FIG. 3 shows a schematic diagram of a typical power factor correctioncircuit (PFC) 12 of the PRIOR ART. Pulsating DC voltage on node 15 isconverted to a DC voltage on node 16 by action of integrated circuit ICchip 24. For illustrative purposes the IC will be preferably a L6561 ICmade by ST Microelectronics. There are several other PFC chips on themarket with similar functions that can be adapted for alternative use.With the proper choice of circuit parameters, the PFC action can be madeto perform reasonably well over a wide range of applied AC linevoltages.

The boost function is accomplished by the charge-discharge action ofboost inductor 25 caused by the repeated high frequency switching ofpower MOSFET 27. Boost inductor 25 is charged with magnetic energyduring the interval when MOSFET 27 is switched on and current flows toground from node 55. When MOSFET 27 switch opens, the magnetic field ininductor 25 collapses causing the voltage on node 55 to increasesufficiently high above the voltage on node 16 to produce current flowinto storage capacitors 28 and 29 and into the load circuit connected tonode 16. A scaled down sample of the DC voltage at node 16 is applied tothe IC 24 at pin 1. A division network consisting of resistors 49, 50,and 51 produces this voltage sample. It is applied to a differentialerror amplifier that is part of a voltage controlling servo loop.Compensation network 44, 45, and 46 integrate the detected error signalas part of this servo loop. The charging current through boost inductoris sensed by sense resistor 48 and applied to IC 24 on pin 4 as an inputto a control comparator within the internal circuitry of IC 24. Divisionnetwork 31, 32, 33, and 34 presents a scaled down sample of the incomingpulsating DC waveform to the IC 24 at pin 3 so that in internalcircuitry can control the MOSFET 27 on time so that the average currentinto node 15 matches the shape of the voltage at node 15. A scaledsample of the voltage across the boost inductor is produced by a fewsecondary turns connected to node 52. A sample is presented to the IC 24at pin 5 through current limiting resistor 37 for timing purposes. Theclamped full wave rectifier consisting of components 38, 39, 40, 41, 42,43, and 53 produces a DC voltage needed to energize the IC 24 at node54. Resistors 35 and 36 provide a small current that is used to energizethe chip upon initial starting of the circuit after power is firstturned on.

As shown in the schematic diagram of FIG. 4, there is a sine waveinverter as used in many PRIOR ART electronic ballasts. The circuit canbe described as a current-fed bipolar self-oscillating half-bridge sinewave inverter. Oscillating current flows back and forth through wire 71energizing the parallel resonant tank circuit consisting of the primaryinductance T1P, primary capacitor CP, and the reflected secondary loadof the lamps 14 in series with ballasting capacitors CBA, CBB, and CBC.The oscillating drive current in wire 71 passes through the paralleltank circuit into blocking capacitor 56 and returns to the supply at themidpoint 30 of the two series filter capacitors 28 and 29 (as shown inFIG. 3). The oscillating drive current in wire 71 is forced through thetank circuit load from the DC supply voltage 16 by means of clampedtransistor switches, QH and QL, being protected by reversed biasedrectifiers DH and DL, respectively. The transistor switches QH and QLare switched ON and OFF by means of the sine wave voltages from windingsT1H and T1L through the shaping networks of 57–64. The two windingisolation choke T2 helps form a constant current back and forth squarewave load into wire 71. Transient suppressor network TS removeexcessively large voltage spikes from choke T1. The Diac network,comprised of Diac 69, resistors 65, 66, 67, and 70, and capacitor 68,generates a sharp current into the base of QL to initiate oscillationwhen the ballast is first turned on, or after any cessation ofoscillation that sometimes occurs during lamp ignition. When power isfirst applied, the full open circuit voltage is applied to the lamps.After ignition, the voltage across the lamps drops to a significantlylower value. The voltage from winding T1S remains substantially the samewith the ballast capacitors CBA, CBB, CBC, dropping a significantamount. With most of the voltage drop occurring across the ballastcapacitors, the current flow into the lamps is little affected byimpedance changes of the lamps, thus stabilizing the lamp operation.

FIGS. 5–8 show the detail of the preferred embodiment. FIG. 5 is aschematic diagram of an improved PFC circuit. The improved circuit ofFIG. 5 differs from the prior art schematic of FIG. 3 in the circuitryin Outlines 72, 73, and 80. Outline 80 is part of the circuit functionthat turns the inverter ON and OFF in a cyclic fashion when a no lampcondition is detected. This circuit function will be discussed belowalong with the discussion of FIG. 11. Outlines 72 and 73 involve theconnection to pin 3 of IC 24. The new components involved are 74–77 andare shown in the circuit fragment illustrated in FIG. 6. The inventivecircuit needs to maintain good PFC performance over a wide or universalrange of incoming AC line voltages. The incoming rectified waveformsshown in Graph C in FIG. 6 are for the two extreme applied AC linevoltages, for example, 120 and 277 volts. The signal that is required bythe chip to shape the AC load current so that it matches the input ACvoltage is the scaled input to pin 3 of IC 24, a connection known as themultiplier input. Because of the input characteristics of the multipliercircuit connected to pin 3, it is found that in prior art PFC circuitsthat the Third Harmonic Distortion (THD) is significantly higher at thehigher AC line voltages that can be used in a universal input voltageballast, for example, 277 volts. The novel circuit of FIG. 6 improvesthe performance and lowers Total Harmonic Distortion (THD) of thecorrected line current at the higher line voltages by adding a small DCoffset voltage to the pulsating AC input that is only present at thehigher line voltages. This DC offset places the larger waveform into amore linear region of operation. This offset raises the input signal aslight amount above the zero voltage position, (refer to Waveform “A” ofFIG. 6). This offset only occurs for line voltages above a thresholdvalue due to action of the Zener diode 74 and the filter composed ofcomponents 75 and 76, producing the Waveforms “B” shown in the FIG. 6.Waveforms “C” show the incoming pulsating DC signal: note that there isno offset voltage. An enlarged plot of the multiplier waveform input isshown in FIG. 7.

A problem that sometimes can occur in the prior art sine wave inverterof FIG. 4 is illustrated in FIG. 8. In this figure, the current pathsare shown at the end of a switch interval when transistor QL, shown inthe figure as a closed switch, is about to switch open and transistorswitch QH, shown as open in the figure, is about to switch to the ONstate. A complementary situation occurs during the next switch interval,when the states of QH and QL are interchanged, and similar paths withreversed direction are set up involving elements reflected across theline of symmetry of the schematic. For simplicity, the discussion willbe directed only to one half of the oscillatory cycle. During the steadyportion of the switching interval when switch QL is closed, the mainflow of power through the circuit is by means of current path L. Duringthis interval, parasitic current HP is absent, and the inductance of thelower winding T2L of isolation choke T2 causes inductive limiting ofcurrent L. Current path L takes the current from the parallel resonanttank circuit TC, composed of transformer primary T1P and the combinedimpedance of capacitances and load resistances represented in thisfigure as CP(TOT), through closed switch QL, the lower winding T2L ofisolation choke T2, and into ground and into capacitor 29. Dischargecurrent flows out of capacitors 29 and 30 through current path R, backto tank circuit TC. Current paths from the supply node and ground nodeare also present but are not shown for simplicity. They serve to provideincoming energy to overcome losses in the circuit elements and the loadbeing driven. A significant unwanted current impulse HP sometimes occursnear the time when the states of switches QL and QH are about to beinterchanged, that is the main switch time. If it happens that duringthis situation that the voltage of node 91 rises sufficiently above thatof the output of the upper winding of isolation choke T2, then bypassdiode DH which has been in the open or reversed biased state until nowcan conduct, causing parasitic current HP to flow. By transformer actionan additional current component that matches HP is added to current L.Because of the phasing of the windings of isolation choke T2, thiscurrent component is in the same direction as L. These parasiticcurrents combine and return to the tank circuit through path R.Isolation choke T2 has tightly coupled windings and thus provides noimpedance to these signals. Thus, for a brief interval, a short circuitis placed across the tank circuit TC, causing a large unwanted parasiticcurrent transient that can cause a significant overheating of thecomponents involved.

This shoot-through current is unique to current fed circuits of thistype and differs from the shoot-through current commonly seen in voltagefed half bridge circuits. It can cause circuit failure if notcontrolled. In the preferred embodiment, shown in FIG. 9, diode-resistorparallel circuit elements shown in Outlines 78 and 79 serve to minimizethe above mentioned parasitic currents, and thus reduce circuit heatingso that the useful life and reliability of the inverter can be improved.The details of the circuit action are shown in FIG. 10. For the sameswitching state as discussed above whereby switch QL is closed, diode 81becomes reversed biased during the transient interval, and any parasiticcurrent is effectively reduced by bypass resistor 81, reducing theheating effect on the remaining circuit elements. During thecomplementary switch interval when the states of QH and QL areinterchanged, the main power flow is through diode 81, causing littlepower loss, and the diode-resistor pair represented in Outline 78 servethe same purpose as Outline 79 did during the previous switch interval.Thus, normal circuit function proceeds with reduced parasitic currents.

The last novel feature is the mechanism used to cycle the inverter at aslow periodic rate during a condition when the ballast is energized withAC power, but no lamps or defective lamps are present. This feature hasnot generally been used in the lighting industry for instant startballasts, but adds to product reliability as it reduces circuittemperatures during a circuit operation mode that as the potential forcausing overheating. This mechanism is shown as Outline 80 of FIG. 9,and FIG. 11. The first part of the circuit is the MOSFET Switch 85 inOutline 80 of FIG. 9. The gate of MOSFET 85 is controlled by a dc signalthat is a rectified, filtered version of the main PFC MOSFET 27 gatedrive signal on pin 7 of IC 24, node 90 on the schematic of FIG. 9. Thissignal is only present in a steady fashion when the PFC circuit isdelivering power to a load. When the boost converter is disabled, thegate drive 90 is held at zero and an increased voltage drop resultsacross capacitor 56 that causes the AC voltage at node 30A of FIGS. 9and 11 increases in magnitude. The DC voltage at node 30A is blocked bymeans of capacitor 96 of FIG. 11. The coupled AC waveform is thanconverted into a DC control voltage by rectifier-filter 92 and appliedto the base of small signal transistor 106 via circuit elements in 94.This base drive saturates transistor 106, and effectively grounds theanode of unijunction UJT transistor 108. The UJT transistor 108 is wiredas a relaxation circuit shown in Outline 93. If the lamps are removedfrom the ballast, the AC signal at node 30A decreases sharply, therectified output from the rectifier-filter 92 approaches zero, andtransistor switch 106 opens so that capacitor 107 can slowly chargethrough resistor 109. Resistor 109 is connected to the PFC IC supply,signal 54 of FIG. 5. When the anode voltage of UJT 108 exceeds its gatevoltage by a slight amount, then the UJT 108 anode-cathode pathwayconducts, and a strong current pulse is injected into the base ofDarlington transistor 95. This transistor provides a low resistanceacross the IC 24 chip supply filter capacitors 43 of FIG. 5, dischargingthem, reducing IC 24 supply voltage to a low value, and disabling thePFC IC 24. When disabled, the gate signal 90 stops, shutting off theinverter via MOSFET circuit in Outline 80. When capacitor 107 fullydischarges, the UJT 108 opens and the IC chip supply slowly charges.When the chip supply on-threshold voltage is reached, PFC operationrestarts, and the inverter shut-off MOSFET switch 85 closes, allowingDiac circuit 114 to restart inverter operation. If no lamps areconnected the entire cycle repeats again and again. The cyclic removalof power from the PFC and inverter stages during part of the repeatcycle provides for lower internal component temperatures that add to theoverall reliability of the product.

It should be understood that there may be numerous modifications,advances or changes that can be made to the present invention, but indoing so, it is intended that they should not detract from the truespirit of the present invention.

1. An electronic ballast capable of energizing a plurality of gasdischarge lamps connected in a parallel configuration comprising a powerfactor correcting boost converter capable of being used over a widerange of alternating current (AC) line voltages to provide regulatedpower to a self-oscillating sine wave inverter that drives the pluralityof gas discharge lamps at high frequencies, and at least onediode-resistor parallel circuit within said self-oscillating sine waveinverter to minimize parasitic currents and reduce circuit heating, andsaid power factor correcting boost converter including a Zener diodebased coupling circuit which adds a direct current (DC) offset tosampled alternating current (AC) line voltages.
 2. The electronicballast capable of energizing a plurality of gas discharge lampsconnected in a parallel configuration in accordance with claim 1,wherein said at least one diode-resistor parallel circuit includes atleast one diode and a bypass resistor.
 3. The electronic ballast capableof energizing a plurality of gas discharge lamps connected in a parallelconfiguration in accordance with claim 1, further including a firstdiode-resistor parallel circuit and a second diode-resistor parallelcircuit to minimize parasitic currents and reduce circuit heating. 4.The electronic ballast capable of energizing a plurality of gasdischarge lamps connected in a parallel configuration in accordance withclaim 1, wherein said Zener diode is serially connected to form acoupling circuit, that includes at least one Zener diode and a filterincluding at least one capacitor and at least one resistor.
 5. Aninstant start electronic ballast that energizes a plurality of gasdischarge lamps connected in parallel comprising a mechanism that cyclesa self-oscillating half-bridge inverter on and off at a slow periodicrate, under control of a zero lamp sense circuit; wherein a MOSFETswitch provides a steady gate signal while delivering power to a load,but is switched off when its boost converter is disabled, stopping theinverter oscillation during a condition when said plurality of gasdischarge lamps is electrically connected, but no lamps, defective orinoperative lamps are present resulting in a reduction of circuittemperatures in said condition; wherein said mechanism repeats the onand off cycle until restoration of the load, whereupon the MOSFET switchcloses and a diac circuit restarts operation of said half-bridgeinverter; and normal operation is resumed upon installation of a newlamp, without disconnection and reconnection of an AC power source. 6.An electronic ballast capable of energizing a plurality of gas dischargelamps connected in a parallel configuration comprising: a. a powerfactor correcting boost converter capable of being used over a widerange of alternating current (AC) line voltages to provide regulatedpower to a self-oscillating sine wave inverter that drives the pluralityof gas discharge lamps at high frequencies, said power factor correctingboost converter including a Zener diode based coupling circuit whichadds a direct current (DC) offset to sampled alternating current (AC)line voltages; b. a mechanism capable of cycling an inverter on and offat a periodic rate during a condition when the electronic ballast isenergized with alternating current (AC), when said plurality ofgas-discharge lamps is electrically connected but inoperative; and c.further including at least one diode-resistor parallel circuit tominimize parasitic currents and reduce circuit heating.
 7. Theelectronic ballast capable of energizing a plurality of gas dischargelamps connected in a parallel configuration in accordance with claim 6,wherein said at least one diode-resistor parallel circuit includes atleast one diode and a bypass resistor.
 8. The electronic ballast capableof energizing a plurality of gas discharge lamps connected in a parallelconfiguration in accordance with claim 6, further including a firstdiode-resistor parallel circuit and a second diode-resistor parallelcircuit to minimize parasitic currents and reduce circuit heating. 9.The electronic ballast capable of energizing a plurality of gasdischarge lamps connected in a parallel configuration in accordance withclaim 6, wherein said a serially connected Zener diode based couplingcircuit includes at least one Zener diode and a filter including atleast one capacitor and at least one resistor.
 10. The electronicballast capable of energizing a plurality of gas discharge lampsconnected in a parallel configuration in accordance with claim 6,wherein said mechanism includes a MOSFET switch controlled by rectifieddirect current (DC).
 11. The electronic ballast capable of energizing aplurality of gas discharge lamps connected in a parallel configurationin accordance with claim 10, wherein the voltage to said MOSFET switchis provided by a diode and a filtered voltage divider.
 12. Theelectronic ballast capable of energizing a plurality of gas dischargelamps connected in a parallel configuration in accordance with claim 11,further including a diac circuit which acts to restart the operation ofsaid inverter.
 13. The electronic ballast capable of energizing aplurality of gas discharge lamps connected in a parallel configurationin accordance with claim 6, further including a diac circuit which actsto restart the operation of said inverter.
 14. A circuit for exciting aplurality of gas-discharge lamps comprising: a. a first subcircuit torectify a first alternating current (AC) voltage forming a pulsating DCvoltage; b. a power factor correction subcircuit to boost said pulsatingDC voltage to form a higher DC voltage; c. a third subcircuit to convertsaid higher DC voltage to a second AC voltage for exciting saidplurality of gas-discharge lamps, wherein a frequency of said second ACvoltage is higher than a frequency of the first AC voltage; and d. saidpower factor correction subcircuit further comprising circuitry toperiodically interrupt power to said third subcircuit when a zero lampstate is detected.
 15. The circuit for exciting a plurality ofgas-discharge lamps as recited in claim 14, wherein said power factorcorrecting boost converter periodically interrupts the power to saidthird subcircuit when said plurality of gas-discharge lamps iselectrically disconnected from said circuit.
 16. The circuit forexciting a plurality of gas-discharge lamps as recited in claim 14,wherein said power factor correcting boost converter periodicallyinterrupts the power to said third subcircuit—when one or more of saidplurality of gas-discharge lamps is absent or inoperative.
 17. Thecircuit for exciting a plurality of gas-discharge lamps as recited inclaim 14, wherein said plurality of gas-discharge lamps are connected ina parallel configuration.
 18. A circuit for exciting a plurality ofgas-discharge lamps comprising: a. a first subcircuit to rectify a firstalternating current (AC) voltage forming a rectified voltage; b. a powerfactor correction subcircuit to boost said rectified voltage; c. a thirdsubcircuit to convert said boosted rectified voltage to a second ACvoltage for exciting said plurality of gas-discharge lamps, wherein afrequency of said second AC voltage is higher than a frequency of a saidfirst AC voltage; and d. said third subcircuit further comprising aplurality of switching devices, an isolation choke, and a plurality oftransient parasitic current limiting circuits to limit the transientparasitic current through said plurality of switching devices; at leastone of said transient parasitic current limiting circuits comprising adiode and resistor connected in parallel that minimize the parasiticcurrent, reduce circuit heating and provide an increase in reliabilityand useful life of the circuit; wherein said plurality oftransient-parasitic current limiting circuits is connected between eachof said plurality of switching devices and said isolation choke.
 19. Thecircuit for exciting a plurality of gas-discharge lamps as recited inclaim 18, wherein each of said plurality of transient parasitic currentlimiting circuits comprises a diode.
 20. The circuit for exciting aplurality of gas-discharge lamps as recited in claim 19, wherein each ofsaid plurality of transient parasitic current limiting circuitscomprises a resistor.
 21. The circuit for exciting a plurality ofgas-discharge lamps as recited in claim 20, wherein said plurality ofswitching devices are bipolar transistors.
 22. The circuit for excitinga plurality of gas-discharge lamps as recited in claim 20, wherein saidplurality of switching devices are MOSFETs.
 23. The circuit for excitinga plurality of gas-discharge lamps as recited in claim 18 wherein saidplurality of gas-discharge lamps are connected in a parallelconfiguration.
 24. An inverter circuit comprising: a. first and secondswitching devices connected in series; b. a positive feedback device foreach of said switching devices arranged to provide alternate switchingof said first and second switching devices; c. an isolation choke toprovide current limiting; d. a starting circuit to initiate oscillation;e. bypass diodes to prevent reverse currents from flowing through saidfirst and second switching devices; f. first and second transientparasitic current limiting circuits; and g. a resonant coupling deviceto transfer power to a load; each of said first and second transientparasitic current limiting circuits, at least one of said transientparasitic current limiting circuits comprising a diode and resistorconnected in parallel, connected between each of said first and secondswitching devices and said isolation choke to limit the transientparasitic current through said first and second switching devices. 25.The inverter circuit as recited in claim 24, wherein said first andsecond switching devices are bipolar transistors.
 26. The invertercircuit as recited in claim 24, wherein said first and second switchingdevices are MOSFETs.
 27. The inverter circuit as recited in claim 24,wherein each of said first and second transient parasitic currentlimiting circuits comprises a diode.
 28. The inverter circuit as recitedin claim 24, wherein each of said first and second transient parasiticcurrent limiting circuits comprises a resistor.